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The creek has multiple high points, and much of it becomes stagnant for months during the summer. A single footstep reveals the darker layers just a few inches down.

I just came back from a weekend at the ocean, and I saw the very same thing while walking on the beach. You dig down about an inch in the sand, and you see a dark layer that looks just like the dark layer in my freshwater dsb. You notice a slight sulfur smell, too, which I experienced briefly in my tank while the substrate cycled.

The spot where I vacation has the most diversity of sea life anywhere in the world (I started to list all the species, but it got long and obnoxious, so just know that every sea thing imaginable lives there), therefore I'm positive the sand there is in top health, and the dark layer is normal, not deadly. I'm glad you can affirm the same thing in freshwater!

And now (sorry in advance) I'd like to indulge in a long-winded and mildly pompous rant of my own:

I really think the main secret to keeping a freshwater DSB is to never shock the substrate. The DSB is so easy, and so worth having, as long as you can follow that one safety rule. The nightmarish die-offs of legend and song were probably the result of somebody doing serious trauma to their dsb without removing their animals first.

The DSB does a wonderful job of keeping it's toxic elements confined to the lowest layers, and detoxifying those elements before they can reach the water. Intentionally stirring the sand is unecessary, counterproductive, and if done with too much enthusiasm, possibly even deadly to your creatures. All you need are some burrowing snails, clams, worms, or fish that will slowly and gently aerate the sand for you, so you can just sit back and leave it up to them.

So many people's aquariums could benefit from DSB filtration in freshwater, but it might not be for those folks who try hard to keep their tanks as clean as they can, because they will have to learn to relax their tank vacuuming habits for the health of the sand bed. Nature isn't clean, a certain amount of mulm is beneficial and needed if you want to keep fish as well as nature does.

Not disrupting the DSB also means uprooting plants as little as possible, so if you're impulsive like me, your DSB will teach you a certain amount of patience. I do plan on moving some plants in my aquarium soon, but I am going try to space the job out: carefully move a couple plants today, a couple tomorrow, so the sand bed stays as intact as possible. DeeDeeK, as you know from reading this thread, prefers to simply cut the roots off and leave them in the substrate, I will probably do that with my water wisteria. If Heaven forbid, I ever do have to really dig around in the sand a whole lot, I will certainly take the precaution of moving my aquatic friends out of harms way beforehand. End of my blabbering. For now.

Last edited by Anoxia; 03-03-2010 at 4:20 PM.
Reason: added an "s" that was missing

The nightmarish die-offs of legend and song were probably the result of somebody doing serious trauma to their dsb without removing their animals first.

The DSB does a wonderful job of keeping it's toxic elements confined to the lowest layers, and detoxifying those elements before they can reach the water.

Not disrupting the DSB also means uprooting plants as little as possible, so if you're impulsive like me, your DSB will teach you a certain amount of patience. I do plan on moving some plants in my aquarium soon, but I am going try to space the job out: carefully move a couple plants today, a couple tomorrow, so the sand bed stays as intact as possible. DeeDeeK, as you know from reading this thread, prefers to simply cut the roots off and leave them in the substrate,

I might further add to the mention of nightmarish die-offs of legend and the DSB's doing a wonderful job of detoxifying those elements before they can reach the water by pointing out that if bubbles are forming in a region of substrate, that means the water in there is already saturated and will absorb no further gas - in other words, diffusion is limited enough to concentrate the gas near its source. The water is what carries the toxic gasses etc., not the bubbles which rise from the substrate.

In a really nice, loosey-goosey sand bed, the toxins can actually diffuse rapidly enough into the regions where nitrate-reducing and aerobic bacteria can eat it all up. If, in this case, the anoxic/strongly anaerobic zone is disrupted and exposed to the water column, things'll be fine. So, what we want is for hydrogen sulfide and other toxins to seep constantly out of the non-aerobic regions.

Myself, I am a bit cavalier about moving plants around but it is true, those with extensive root systems get cut off where stem joins root. Trying to re-bury roots is frankly a pain to do well and to just jam 'em all in together results in much root melting so you might as well cut them off (or just trim them if the plant can't just regrow its roots) if you don't want to carefully bury them which disrupts much substrate.

Short of releasing saturated toxic substances into the water column, disrupting the sand has definite disadvantages, especially when the disruption extends into more than one zone aerobic and anaerobic/anoxic activity. First of all, if oxygen is introduce into either non-aerobic zone, the bacteria either switch to oxygen-based metabolism and stop doing certain useful things like denitrifying, or the bacteria can simply die. Also, if the aerobic zone becomes temporarily anaerobic, nitrifying bacteria will die en masse. Then it takes days for the oxygen to either return or to be exhausted and bacteria to either switch back, recover, or recolonize, and for diffusion to return to normal.

If you're like me and blindly have faith that your substrate is not saturated with poison anywhere, you probably move your plants around at will, with the understanding that the more you disrupt the substrate, the less bioload your DSB will carry. Don't forget that the DSB can carry quite a high bioload, given time to adjust. Even taking out a good fraction of its capacity can be done with little or no consequences to its practical capacity unless you have the tank very close to the DSB's maximum capacity already.

I forgot whether I mentioned this idea yet in this thread so here goes: As plants grow, they absorb carbon in the form of CO2 and it is used as a building block in the complex organic molecules the plant synthesizes and builds its tissues from while the oxygen is released. In other words, the plant is warehousing carbon, as well as the minerals it absorbs, in all of itself. So, when the plant dies, that stocked-up carbon is released, largely as CO2! The minerals likewise are released.

Buried in the substrate, the roots will decay slowly and CO2 and minerals will steadily diffuse into the sand. That CO2 will enter the water column and boost dissolved CO2 levels. I haven't measured the difference it makes, in terms of ppm non-DSB vs DSB but would like to. A friend measured my tank and said it was 9ppm, short of the 15ppm levels used in Dutch tanks buy enough to seriously enhance plant growth. I plan on buying my own CO2 kit and figuring it all out. Also, it's time to study the use of CO2 in planted aquaria (study in a planted aquarium?)(ha ha ha).

So, to attempt to explain myself more simply and clearly, if the plants are growing in a tank which only gets its CO2 from the atmosphere, they absorb it from the water and the air replenishes it. Duh. But now the tank contains the CO2 from the air and the carbon stored as plant tissue. So, the potential CO2 grows and grows until removal of the plants(including root system) by the aquarist counterbalances it. Leaving root systems in the sand allows the potential CO2 to grow until the aquarist decides to start removing them and a new equilibrium is reached.

As the severed roots decay, the rate of decay regulates the release of CO2. If new root systems are left behind to decay at the same rate that carbon is released from the substrate, the result will be a steady, consistent level of CO2 in the water and a steady balance of potential CO2 stored in the sand as the various carbon compounds roots are made of.

I favor Cabomba Caroliniana and Eichhornia Diversifolia (variable leaf water hyacinth) as attractive plants which develop extensive root systems and tolerate being severed at the roots and replanted very well. There are probably tons of others which are equally good. I just stick the stems back in right in the middle of the root system, next to the little stump. They grow very very well that way.

Be careful when you fight the monsters, lest you become one - Nietzsche

So the theoretical die-off scenario would probably be the result of a lack of oxygen, instead of pollution? I almost want to establish a nicely seasoned DSB (without animals), and then intentionally scramble the heck out of it, just so I can test what happens to the water afterwards. Though without the digging critters, I suppose that wouldn't be a proper DSB.

I don't want to add fuel to the false idea that it's dangerous to have deep sand in your tank, though. If anything, it makes your aquarium safer, because it's more stable, like Anti Decent just described before me.

So the theoretical die-off scenario would probably be the result of a lack of oxygen, instead of pollution? I almost want to establish a nicely seasoned DSB (without animals), and then intentionally scramble the heck out of it, just so I can test what happens to the water afterwards. Though without the digging critters, I suppose that wouldn't be a proper DSB.

I don't want to add fuel to the false idea that it's dangerous to have deep sand in your tank, though. If anything, it makes your aquarium safer, because it's more stable, like Anti Decent just described before me.

The theoretical die-off would be the result of a, for instance, blast of water saturated (or nearly so) with H2S, resulting in H2S poisoning. The quantity of water in those few cubic centimeters of sand, even completely devoid of oxygen, would average together with the oxygenated water column, thousands or millions of times greater, to virtually the same oxygen level as the water column pre-contamination. Hydrogen sulfide (H2S) is very toxic to animals and (this is hypothetical) the volume of water in a few cubic centimeters of sand (remember that 1cc of water = 1ml, so we're talking a fraction of a milliliter within the sand) may be able to carry a lethal dosage for the tank. Too much science in that for my meager research skills!

Honestly, I disturb my DSB very frequently. I'm just that sort of hypocrite No no, but seriously, it's not so often that the disturbed areas don't have a chance to stabilize again, and I'm sure that I don't mess up even 20% of it at a time and mostly around 5% of it at a time. Most of this energy is spent trying to get my bed of milfoil just so or jamming a cut-off root system a little deeper into the sand so as the stump is completely buried.

What is dangerous is a sand bed made of sand which allows for insufficient diffusion of dissolved gasses and other solutes. Also, such a sand bed will not grow very fertile since mulm cannot infiltrate it and leaving root systems will certainly generate problematic anaerobic/anoxic areas.

Be careful when you fight the monsters, lest you become one - Nietzsche

Anoxia, I don't feel like you'd be creating any anti-DSB feelings in any one.
In the interests of science, I encourage it. However, If I tore apart a filter pad from my hob on the 45gallon, and dumped it into the water, I'm sure it would cause some sort of massive fluctuations. But then, I'm not the expert here.

I've been away for a few days visiting family, had some one else feed my MTS in the DSB. I left... Wednesday? I believe and came back Sunday. They gave them flakes instead of sinking pellets, but I digress.

Before I left, I "seeded" the DSB with a few injections of material I acquired from my puffers aquarium, and a small amount of water from another tank.

I wish I had a better camera.

I return to find water fleas, and other 'micro' life scurrying across the glass. Tiny white free living worms inching by, and what I've deemed, swimming sand, (generic term I use when I'm telling other people what to look for) were one thing, but I also found something Ive not seen in any of my aquariums before, ever. Slightly thicker than a hair, pink little worms, buried in the sand, with only a small part of their body sticking out, furiously flicking away at the water. I gently taped the glass, causing the worms to bolt under the sand.
They seem to be vertically orientated, and return to the surface rather quickly. There is only a few of them that I can see, however they are very hard to find.
They are round, not flattened. There is one against the glass now, about half an inch down, slowly picking its way through the sand. My camera can't focus on something so small. I've no idea what they are. Tubifex are much bigger, and I've never put live ones into any of my set ups. They must be in the puffers tank as well, come in on some of the plants, or in the soil I used for the bottom layer.

Any ideas on what they are? They seem to enjoy the sand bed.

-note- I was unable to get into the creek. Snow melt has the water up.

-change- Before leaving I added a huge air stone to circulate water, feeling that a pump might kill tiny organisms that it sucks in.

... Though without the digging critters, I suppose that wouldn't be a proper DSB...

You know, I think you can call a DSB a proper DSB so long as it denitrifies as well as denitrifies and (if it is in a planted tank) provides a fertile substrate to root in. I personally believe in a planted DSB with digging critters as the best way to achieve the most in terms of biofiltration.

I recently got ahold of some sand which is almost, but not quite gravel. It's max. size is about 1mm across. It packs down about as tightly as popcorn, and I'm experimenting with it using food dye, which I inject into a mini DSB in a jar with 2 inch hypodermic needle In order to see how it diffuses. I'll tell you, this sand needs no help from burrowing critters! Actually, I think it needs to be deeper, like 4.5" or 5", to develop sufficient anaerobic regions. I wish I had an aquarium I could set up with this stuff.

Of course no sand comes in a perfectly uniform grain size, but we can buy sand which has been meshed to exclude all but a limited range of sizes. Pool filter sand is what I now advocate rather than river sand because of the ready accessibility of pool filter sand, which happens to be meshed - it is meant to be open to water movement and therefore is open to diffusion.

Anyhow, large grains = less or no need for burrowers but at price of diminished surface area for the bacteria of the biofilter to live on, i.e. the biofilter's maximum capacity is smaller. Small grains = more need or even dependence upon burrowers , tremendous surface area.

I would like to try a very deep sand bed of large (~1mm) grained sand. A VDSB would be 5+inches. I wouldn't plant in it or include any burrowers. I bet it would work, nitrifying and denitrifying, eating up its own hydrogen sulfide and all. I also be it would still do better with at least plants and some kinda critters which would munch up and break down mulm into super-small particles.

Be careful when you fight the monsters, lest you become one - Nietzsche

Let me know if I suggest anything wrong, I may be speaking without up to date knowledge here.

Food dye, to me anyways, doesn't feel like a proper medium to test with. If all your looking for is just its pathing through the sand, then yes, but organic material that would typically be passing through tends to be much larger than a couple of molecules. Try getting multiple jars, pickle jars would work, and filling each one with different sized grains of sand/gravel, and allowing them to cycle. Introduce multiple types of standard organic materials that would be present within an aquarium, and see how long it takes bacteria to break them down and send them through the substrate. This is obviously a somewhat long term test. And to be more thurough, a duplicate jar, with organisms, planeria, and and the like, could also be used.

Playsand, along with other things, can be used to rig a freshwater filter to make drinkable water, the sand itself capturing the particulate matter and storing it within the layer. However gravity is forcibly pulling the material and water through the system, not daily environmental processes. So even very small grains should work, just require more time for things to seep down into them. Which is where organisms come in.

The MTS in my sand bed seem to be doing a good job at completely processing all the food introduced into the tank. Their tiny string droppings disappear after about day as well. I have yet to see dark sand form, granted it has been only about a week and I did seed the bed. Tonight I will push a piece of pellet food into the bed along the glass, at 3 different levels, and observe them over time, to see if all create black sand, or just one or two, and which one goes first.

Let me know if I suggest anything wrong, I may be speaking without up to date knowledge here.

So might I!

Originally Posted by Gammarus

Food dye, to me anyways, doesn't feel like a proper medium to test with. If all your looking for is just its pathing through the sand, then yes, but organic material that would typically be passing through tends to be much larger than a couple of molecules.

I agree! I simply have been considering the diffusion of solutes, not the infiltration of solids, through the sand bed.

Originally Posted by Gammarus

Try getting multiple jars, pickle jars would work, and filling each one with different sized grains of sand/gravel, and allowing them to cycle. Introduce multiple types of standard organic materials that would be present within an aquarium, and see how long it takes bacteria to break them down and send them through the substrate. This is obviously a somewhat long term test. And to be more thurough, a duplicate jar, with organisms, planeria, and and the like, could also be used.

Excellent suggestion! I would like to add an oxygen probe, microscope, and some method of identifying organic molecules as well as bacteria, in order to really dissect the sand beds!

Frankly, I go by one part education, one part investigation, and ten parts inspiration( ) when I am making decisions re. sand beds in my tanks. Honestly, I just sound like I know what's going on!

Originally Posted by Gammarus

Playsand, along with other things, can be used to rig a freshwater filter to make drinkable water, the sand itself capturing the particulate matter and storing it within the layer. However gravity is forcibly pulling the material and water through the system, not daily environmental processes. So even very small grains should work, just require more time for things to seep down into them. Which is where organisms come in.

I agree and I disagree. The issue with smaller grained sands and especially sands with a wide range of grain sizes is not that they truly seal the sand bed to all diffusion/circulation but that the rate of said diffusion is reduced to the point where insufficient oxygen and ammonia, for example, diffuse into the bed for it to perform sufficient nitrification in a given period of time i.e. the ammonia will build up faster than it can be taken out by the biofilter. Also, for the organic compounds which reach the anoxic region, the toxic byproducts of their breakdown can diffuse out so slowly that, say, hydrogen sulfide can reach saturation and begin to come out of solution and form that dreaded bubble of near-pure H2S! If such a beast lifts off and carries sufficient gunk with it or if the fishkeeper stirs it into the water column, there we have one of those apocryphal fish apocalypse stories. Additionally, as you had indicated, critters must help with the infiltration of mulm. Once an animal has helped it on its way, a particle of organic matter must become quite small to infiltrate further, which it will do even more slowly in relation to smaller sand-grain (actually it's the interstices we really are concerned with) sizes than does diffusion. With larger grained sand, the particle size can be of much larger volume and still infiltrate the sand, sifting into it without animal help. As it decays, which it will do rapidly since the easy diffusion keeps things fresh(ish), aerobes aerated to a deeper depth, taking away byproducts of bacterial metabolism, etc., it will break down smaller and smaller and work its way deeper into the sand faster than if the sand had smaller grains.

Now, objections stated, I must agree with you. My objections are based on the viewpoint of a person who keeps fish and shrimp, stocked to fairly high levels. That means a heavy bioload and lots of poo and some left over food. My sand bed needs to work at speed. I'm sure that there are different styles of stocking and aquaria that would work with a lower capacity DSB. I'd imagine something like an Amano-style nature aquarium, but without the high-tech forced growth stuff would work. Maybe it would be like an el Naturalť aquarium but with slower growth. Many many plants fish as an accent. And fine sand LOOKS nicer (imho)! I'd like to figure out the characteristics of sand beds of various grades of sand and have that information on hand to use when deciding what to go with for whatever kind of tank I'm considering making.

Originally Posted by Gammarus

The MTS in my sand bed seem to be doing a good job at completely processing all the food introduced into the tank. Their tiny string droppings disappear after about day as well. I have yet to see dark sand form, granted it has been only about a week and I did seed the bed. Tonight I will push a piece of pellet food into the bed along the glass, at 3 different levels, and observe them over time, to see if all create black sand, or just one or two, and which one goes first.

I've stuck all sorts of things in the sand next to the glass. My favorite was a dead gourami I put way at the bottom. That was almost two years ago and it at one point had a huge anoxic zone around it and even today there's a pitch-black oval where the body was. Stick some roots next to the glass and watch 'em!

If you dig up some root systems in a DSB with blackworms in it, you'll find worms all the way into the deep anaerobic regions, wound amongst the roots, without their tails sticking up into the water column. I believe they're taking their oxygen from the roots! No kiddin'!

Be careful when you fight the monsters, lest you become one - Nietzsche